A variety of structures are routinely inspected to determine the health of the structure and to identify any issues that may require further inspection, maintenance or repair. For example, buildings, bridges and the like may be regularly inspected to identify the onset of any issues that may potentially weaken or otherwise eventually render the structure unsuitable for its intended use. Similarly, vehicles, such as airplanes, trains, ships and the like, may be regularly inspected in order to identify any issues that merit further inspection, maintenance or repair.
In instances in which the inspection of a structure determines that the structure should undergo maintenance or repair, such as to address a structural anomaly identified during the inspection, the maintenance activities or other repairs are desirably performed in a timely manner such that the structure may be promptly returned to service. For some structures, such as metal or composite aerospace structures, patches have been developed to temporarily repair the aircraft, thereby allowing the aircraft to remain in service until a more opportune time for a more fulsome, but time-consuming repair. Temporary patches offer a number of advantages including a relatively rapid installation and a lower cost than that incurred for a permanent repair. As such, temporary patches may reduce the time that the structure must be out of service following discovery of a structural anomaly and increase the flexibility in scheduling a more permanent repair of the structure.
Temporary patches are generally inspected on a regular basis with inspections generally being conducted more frequently for the temporary patches than the underlying structure. However, inspection of these temporary patches may be burdensome, both from a scheduling and a labor standpoint. To avoid or reduce the costs associated with the inspection of temporary patches, more costly forms of temporary repair may be employed, the lifespan of the temporary patch upon the structure may be limited or the structure may be repaired more permanently. However, these alternatives for avoiding or reducing the costs associated with the inspection of temporary patches effectively reduce at least some of the benefits of utilizing such patches in the first instance.
Temporary patches may be inspected in various manners, including tap testing. In tap testing, the temporary patches are tapped and a technician listens for the resulting tone. Based upon the tone, the technician may identify any underlying structural anomalies, such as a delamination or the like. Unfortunately, some tap testing is subjective and provides no quantitative data for comparative purposes. However, mechanical tap testers exist that do record a signal and can be used to map a value as a function of position. As an alternative to tap testing, infrared thermography or ultrasonic scanning may be employed in order to non-destructively inspect a temporary patch. However, infrared thermography is generally relatively expensive, and ultrasonic scanning generally requires a significant time investment for conducting the test. Furthermore, each of these techniques for inspecting a patch generally requires a technician to regularly access the aircraft, such as via a lift, thereby adding to the time and expense of such inspections.
Another type of inspection for patches introduces structural waves, such as Lamb waves, and one or more sensors, such as piezo-electric sensors, for receiving the waves following propagation through the patch. By analyzing the signals received by the sensors, a determination may be made as to whether the portion of the patch in line between the location of the tap and the sensor is well bonded and intact or whether a structural anomaly was encountered. As a result of the multiple sensors generally included in a patch of this type, the wires required to communicate with the sensors and the hardware, e.g., multiplexor, required to facilitate such communication, the weight and the complexity of this type of patch may be increased more than is desired.
As such, it would be desirable to provide an improved technique for inspecting structures including, for example, the inspection of patches placed upon a structure.